In the times before USB, serial ports were used for lots of computer interconnections. In those days, they were mainly large 25 pin connectors, and adapters for the carious pin cinfigurations were required regularly. For the later 9 pin connectors (around the IBM PC-AT) the adapters were scarce. 

This design attempts to fix that. It requires no additional fasteners or screws, it should just click together and stay together.

The design is tested with PLA and PETG. PLA might not be the first choice here as it tends to deform under stress.

Printed with the defaults of 0.4mm nozzle and 0.2mm layer height. Smaller dimensions will benefit the ridges and make it fit somewhat better, but the defaults are ok.

Designed with OpenSCAD. Printed with a Prusa I3MK3S+ and Mini+.